The invention relates to a machine which is intended for clamping a pipe socket between clamping jaws of a socket screwing-on machine as a function of torque and which consists of a screwing head for clamping and screwing on the socket and of locking tongs fixing the pipe and intended for making screw connections between pipes used especially in the petroleum industry.
On screw-coupling equipment in the petroleum industry, especially on socket screwing-on machines or screw-coupling tongs, clamping systems which clamp nonpositively the article to be clamped and which transmit high torques are used. With an increasing depth and consequently a higher load exerted on the oil-field pipes used, the quality of the screw connection between the socket and the pipe must be improved. The quality of the screw connection is characterized by two features:
1. Obtaining an ideal prestress in the threaded connection,
2. Only slight damage to the pipe and to the socket during the screwing operation.
The screwing torque serves to indicate an ideal prestress in the threaded connection. However, it can serve as an indication of a screw connection of high quality only when the socket has been clamped correctly during the screwing operation. If clamping systems which clamp the pipe socket with a maximum clamping force before the start of screwing are used, the socket experiences elastic deformation. In this case, when the socket is screwed onto the pipe, the theoretical screwing torque is reached sooner than the necessary prestress built up in the threaded connection. In torque-dependent clamping systems, the clamping force increases only when the pipe piece is screwed into the socket. This counteracts a relatively high elastic deformation. The mechanical clamping systems can therefore be divided into two main groups:
1. Clamping systems with a clamping force independent of the torque,
2. Clamping systems with a clamping force dependent on the torque.
The torque-dependent clamping systems are favorable for achieving a high screw-connection quality.
For transmitting the clamping force directly to the socket, all the clamping systems use clamping jaws (clamping pistons) with hardened incorporated or exchangeable knives. In all clamping systems with a torque-dependent clamping force, the peripheral force of the driving torque acts on the clamping jaws via cams or in conjunction with gearwheels and levers and generates the torque-dependent clamping forces.
In many clamping systems, a relative movement resulting in pronounced clamping scores on the socket occurs during the clamping operation between the socket and the clamping jaws. The pipe surface thus acts as a transmission element in the clamping system.
Both clamping systems requiring separate clamping jaws for each socket diameter and clamping systems which, equipped with a single set of clamping means, can clamp sockets of slightly differing diameters are known. The clamping systems known hitherto work in both directions of rotation only when the clamping elements are replaced or changed over.